Method for coating on a substrate



Dc. 8, v1.970 D. 1 HOCHBERG METHOD FOR COATING ON A SUBSTRATE Filed Jan.2e, 196e NVENTOR. DAVU LOUIS HOCHBERG MMJ/. 21

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United States Patent O 3,545,997 METHOD FOR COATING N A SUBSTRATE DavidLouis Hochberg, New York, N.Y., assignor to Pitney-Bowes, Inc.,Stamford, Conn., a corporation of Delaware Filed Jan. 26, 1966, Ser. No.523,054 Int. Cl. B41m 5/18; B44d 1/94, 1/50 U.S. Cl. 117-17 2 ClaimsABSTRACT 0F THE DISCLOSURE This invention relates to a method ofproducing a thermographic transfer printing member which comprisesapplying thermographic ink particles to the topside of a substrate,irradiating the ink from the underside of the substrate and through thesubstrate, whereby a layer of ink is fused to the topside of thesubstrate and then transferring the fused ink layer to a receivingsubstrate which comprises placing the receiving substrate in contactwith the fused ink layer, irradiating the ink layer from the undersideof the substrate through a stencil means and through the substrate,whereby portions of the ink layer are transferred to the receivingsubstrate.

This invention relates to a method for preparing a thermally fusiblecoating on a substrate. The invention further relates to the preparationof a thermographic printing member which may be rejuvenated and resuedin a continuous manner.

A thermographic printing method is disclosed in copending, commonlyassigned application Ser. No. 503,218 of Gilbert Zweig, filed Oct. 23,1965, now abandoned. That method makes use of radiation rich ininfra-red and a stencil master which transmits the radiation in theimage areas but not in the non-image areas. The stencil consists of ametallic coated transparent material known in the art as leafing foil.When such foils are typed upon, the

metallic layer is transferred off in the areas struck by the typewriterkeys to leave transparent image areas and forms a radiation-transmittingstencil.

The stencil is then placed over a heat fusible transfer carbon sheetwhich contains an infra-red absorbing pigment in the carbon layer. Thestencil is placed against the non-carbon side, and a sheet of copy paperis placed next to the carbon side. The stencil is then irradiated with asource of rays which are rich in infra-red which fuses the carbon layerin the image areas and transfers it to the copy sheet to form an imagecorresponding to the stencil image.

After imaging, the transfer carbon is devoid of transfer material-in thetransfer area and has to be discarded and replaced by a new carbon sheetfor the next printing. Thus the necessity of replacing the carbon sheeteach time can be costly.

lt is therefore an object of this invention to provide a thermal carbontransfer medium which may be rejuvenated and reused after each printing.

A further object is to provide a thermal transfer carbon by which thecost of thermal printing may be reduced.

Another object is to provide a method for continuously: forming athermal transfer carbon medium in a thermographic printing process.

Still another object is to prepare a coating of uniform thickness, evenon slightly irregular support material.

A further object is to provide a method for coating a substrate which istransparent to infra-red with a material which is heat absorptive andthermally fusible.

These and other objects of my invention will ,become apparent as thedescription thereof proceeds.

The above objects may be achieved by the use of an endless belt coatedwith a thermographic carbon layer which is used in a thermographicprinting operation and rejuvenated by recoating the used areas of eachprinting operation.

The invention may be better understood by reference to the gure whichshows a cross-sectional View in elevation of the endless belt and theapplication of toner powder, thermographic printing and reapplication oftoner.

A transparent endless belt 1 (made for example of Du Pont Mylarpolyethylene terephthalate) is adapted to travel around rollers 1A and1B. An excess of a thermographic toner powder is deposited on belt 1 at2. The belt with excess toner passes over infra-red lamp 3 in front ofreilector 4 which fuses the toner particles and forms a layer 5 onbelt 1. Excess, unfused toner is removed at 6 either by brush, vacuummeans employing both, gravity, electrostatic forces, or the like.

Belt 1 with fused toner layer 5 is then equivalent to a transfer carbonsheet and is then used for thermographic printing at infra-red lamp 7 infront of reflector 8. For this purpose, a stencil 10, which hastransparent image areas 11 and is non-transparent in the remainingareas, is placed between infra-red lamp 7 and belt 1. A receptor paper12, which may be an envelope, paper sheet or the like on which thestencil image is to be made, is placed in contact with transfer layer 5in register with stencil 10. Stencil 10 is then irradiated with briefbut intense infrared radiation. The layer 5 is fused and transferred toreceptor paper 12.

The fusing radiation from lamp 3 should be less intense than that oflamp 7 at the exposing station. This is done so that the layer fused onbelt 1 by lamp 3 and deposited on the belt will not be so thick thatlamp 7 will not be able to fuse it to effect transfer of the layer frombelt 1 to receptor paper 12.

After the exposure to infra-red lamp 7, the layer on belt 1 has a vacantarea as shown at 13. From this point, belt 1 again comes to the pointfor applying an excess amount of toner at 2A. The toner powder will bedeposited on top of layer 5 except at point 13 where toner will bedeposited on the vacant area and in contact with the surface of belt 1.The entire process is then repeated, fusing the toner in the vacant area13A to form a new continuous layer 11 for thermographic printing.

Although two areas of toner application are shown in the ligure, this isfor illustration. There is actually only one tone applicator since belt1 is continuous and is recycled.

Belt speeds have been varied from between one-half and four feet persecond using 200 watt/inch infra-red lamps but can be increased by useof more powerful lamps.

Belt 1 may be made part of a thermographic printing machine and it willbe obvious that the necessary means for moving belt 1 and for turningthe infra-red lamps on at the proper times for applying the tonerpowder, and feeding stencils and receptor paper may all be provided aswell known in the art to provide a continuous method.

The toner powder used is a thermographic type, i.e. it is readilyfusible under heat. Suitable toners are made by mixing a pigment whichabsorbs infra-red in a molten wax, allowing the wax to harden, andpulverizing the wax and classifying it into a finely divided powder. Assuitable waxes for pebble milling, Castorwax (Baker Castor Oil Co.) wasone such wax. The wax melting point must not be too high since thiswould lead to damaging of the stencil before fusion of the powderoccurs.

Suitable pigments are those whtich absorb appreciable amounts ofinfra-red radiation, such as carbon black and black magnetizable ironoxide.

The amount of pigment can vary from about 5% up to the maximum capableof dispersion in the wax, up to 50% or more. Generally, 20% is quitesatisfactory for good image density and low smearing tendency. Smearingof copy images is worsened by employing lower melting waxes and/ or byincreasing the pigment concentration.

Low melting waxes can be used if they are hard waxes and can be milledin the solid state. They should have a melting point above about 71 C.Some suitable waxes are described in the subsequent specific examples oftoner preparation.

In addition, a fusible toner can be made from readily available resinousmaterials such as shellac and the like, in the same manner.

The following examples describe the preparation of suitablethermographic toner compositions.

EXAMPLE I 80 grams of Castorwax (Baker Castor Oil Co.) having a meltingpoint of 85 C. were placed in a beaker and heated with agitation untilmolten. Then grams of Regal SRF carbon black (Cabot Corp.) and l gram ofArmour PE 200 antistatic agent were blended into the wax while stillmolten until a more or less uniform mixture was obtained. The blend ofwax and carbon black was then poured on a at surface and allowed tosolidify at ambient temperature. The resulting solid mass was thenplaced in a micro pulverizer for about l530 sec., after which it wasplaced in a half-filled pebble mill and milled overnight (about 18hours) until finely pulverized and 7.5 percent of the starting weightpassed through a 400 mesh (75 micron opening) sieve. The resulting 75micron toner power had a fusion temperature of 85 C. (Fisher-Johns)EXAMPLE II In the same manner as described in Example I, 60 grams ofCandelilla Wax (Ross Wax Co.) were combined with grams of nely dividedcarbon black (Regal SRF, Cabot Corp.). 2.4 percent of the linely dividedpowder passed through a 400 mesh sieve and had a fusion point of 71 C.(Fisher-Johns). This amount was useful as a thermographic toner.

EXAMPLE III A thermographic toner powder was produced in the same mannerdescribed in Example I from grams of Castorwax (Baker Castor Oil Co.)and 50 grams IRN 350 magnetic iron oxide (William and Co.) which had amelting point of C. (Fisher-Johns). 4.8 percent passed through a 400mesh sieve and this amount was useful as a thermographic toner.

EXAMPLE IV A thermographic toner powder was prepared as in Example I,from 80 grams of Petrolite WB-S wax (Bareco Wax Co.) and 20 grams Vulcan3 finely divided carbon (Cabot Corp.). The amount of product passingthrough a mesh sieve was useful as a thermographic toner powder and hada melting point 84 C. (Fisher-Johns).

EXAMPLE V Petronauba D wax (Bareco Wax Co.) and Regal SRF finely dividedcarbon were combined as in Example IV, with similar results in obtaininga thermographic toner powder.

EXAMPLE VI Cerathane Polymer 63 (Bareco Wax Co.) was substituted inExample V and the thermographic toner powder obtained had a meltingpoint of 82 C. (Fisher-Johns).

In the same manner as described above, any substrate which is somewhattransparent to infra-red can be coated. Thus even paper as well asnumerous types of plastic sheet materials maybe coated. lt is onlynecessary that the granular or powdered material be heat absorptive andthat the web material be transmissive of infra-red radiation and have adeformation temperature well above the fusion temperature of the coatingmaterial. This can be readily accomplished by mixing carbon black withthe fusible material. The method may therefore be used to produce acoated web by continuously depositing a heat absorptive granular orpowdery material on the surface of the web and heating from below withinfra-red to fuse a layer of the material on the surface of the web. Thecoating thickness is quite uniform because the heat of fusion propagatesthrough the fusible layer of particles for a given distance regardlessof the thickness of the layer of excess fusible particles.

Moreover, although I have described application of thermographic tonerto the belt as a powder, the thermographic toner could be fused onto thebelt by having a solid mass of toner in Contact with the surface of thebelt, and passing radiation from the opposite side of the belt andthrough the belt to fuse the toner.

While I have disclosed certain specific embodiments of my invention,this is only for the purpose of illustration. It will be understood thatvarious changes and modification may be made without departing from thespirit of the disclosure or the scope of the appended claims.

What is claimed is:

1. A method for producing a continuous thermographic transfer printingmember for use in thermographic printing which comprises:

(A) depositing a quantity of a powdered thermographic material incontact with the surface of an endless substrate carrier which istransparent throughout its extent to infra-red radiation,

(B) moving said substrate carrier fwith said material thereon past asource of infra-red radiation disposed on the side of said substratecarrier remote from said thermographic material,

(C) irradiating said thermographic material through said substratecarrier with infra-red radiation to uniformly fuse a layer of saidmaterial to the surface of said substrate carrier,

(D) transferring a part of said layer off of said substrate carrier byirradiating said thermographic material ywith a second source ofinfra-red radiation through said substrate and a stencil placed betweensaid second source of infra-red radiation and said substrate carrier,said second source of infra-red radiation being of a higher intensitythan that used to fuse said thermographic material, the thermographicmaterial irridiated through said stencil and substrate carrier beingtransferred to a receptive sheet placed in contact with saidthermographic material, thereby leaving vacant areas in said layer,

(E) depositing additional thermographic material in contact with saidsubstrate carrier at said vacant areas, and

(F) lagain irradiating said thermographic material with infra-redradiation through said substrate carrier to fuse said additionalmaterial in said vacant areas to reform said uniform layer.

2. A method for producing a continuous thermographic transfer printingmember for use in thermographic printing which comprises:

(A) depositing an excess quantity of a powdered thermographic materialon the surface of an endless substrate carrier which is transparentthroughout its extent to infra-red radiation,

(B) moving said substrate carrier with said material thereon past asource of infra-red radiation disposed on the side of said substratecarrier remote from said thermographic material,

(C) irradiating said thermographic material through said substratecarrier with infra-red radiation to uniformly fuse a continuous layer ofsaid material over the surface of said substrate carrier,

(D) removing excess, unfused material to leave a References Cited layerof uniform thickness on said substrate carrier,

(E) transferring a part of said layer off of said sub- UNITED STATESPATENTS strate carrier by irradiating said thermographic ma- 26776225/1954 Schoufede 117-21X terial with a second source of infra-redradiation 5 2807703 9/1957 Rosh@ 117-175X through said substrate and astencil placed between 2992121 7/1961 Francls et al' 117-36'1 saidsecond source of infra-red radiation and said 3256811 6/1966 Bach117-17X substrate carrier, said second source of infra-red 25037584/1950 Murray 117-37 radiation being of 'a higher intensity than thatused 2503759 4/1950 Murray 117-37 to fuse said therrnographic material,the thermo- 10 2511024 6/1950 Toulmm 117-41 graphic material irradiatedthrough said stencil and 2616961 11/1952 Groak 250`651 substrate carrierbeing transferred to a receptive 2629671 2/1953 Murray? 1178 sheetplaced in contact with said thermographic 2990278 6/1961 Carlson y117-17'5X material, thereby leaving vacant areas in said layer, 301387812/1961 Dessauer 117`17`5X (F) depositing additional thermographicmaterial on 15 3205856 9/1965 Sorensen Irl- 21X said carrier on saidvacant areas, and (G) again irradiating said thermographic material withWILLIAM D' MARTIN Prlmary Exammer nfra-red radiation through saidsubstrate carrier to P- E- ATTAGULE, Assistant Examiner fuse saidadditional material in said vacant areas to reform said continuous layeron said substrate 20 Us' Cl' X-R' carrier. 117-2, 3.2, 17.5, 21, 23,36.1, 226; 250-65

